A. DZY Loves Physics
题目连接：
http://codeforces.com/contest/444/problem/A
Description
DZY loves Physics, and he enjoys calculating density.
Almost everything has density, even a graph. We define the density of a non-directed graph (nodes and edges of the graph have some values) as follows:
where v is the sum of the values of the nodes, e is the sum of the values of the edges.
Once DZY got a graph G, now he wants to find a connected induced subgraph G' of the graph, such that the density of G' is as large as possible.
An induced subgraph G'(V', E') of a graph G(V, E) is a graph that satisfies:
;
edge if and only if , and edge ;
the value of an edge in G' is the same as the value of the corresponding edge in G, so as the value of a node.
Help DZY to find the induced subgraph with maximum density. Note that the induced subgraph you choose must be connected.
Input
The first line contains two space-separated integers n (1 ≤ n ≤ 500), . Integer n represents the number of nodes of the graph G, m represents the number of edges.
The second line contains n space-separated integers xi (1 ≤ xi ≤ 106), where xi represents the value of the i-th node. Consider the graph nodes are numbered from 1 to n.
Each of the next m lines contains three space-separated integers ai, bi, ci (1 ≤ ai < bi ≤ n; 1 ≤ ci ≤ 103), denoting an edge between node ai and bi with value ci. The graph won't contain multiple edges.
Output
Output a real number denoting the answer, with an absolute or relative error of at most 10 - 9.
Sample Input
1 0
1
Sample Output
0.000000000000000
题意
给你一个带边权和带点权的无向图，你需要找到一个最大的子团，使得这个子团的点权和除以边权和最大
题解：
最多选择两个点，这个很容易证明
然后暴力莽一波就好了
代码
#include<bits/stdc++.h>
using namespace std;
const int maxn = 505;
vector<pair<int,double> >E[maxn];
double val[maxn];
int n,m,cnt;
double ans;
int main()
{
scanf("%d%d",&n,&m);
for(int i=1;i<=n;i++)scanf("%lf",&val[i]);
for(int i=1;i<=m;i++)
{
int a,b;double c;
scanf("%d%d%lf",&a,&b,&c);
ans=max(ans,(val[a]+val[b])/c);
}
printf("%.12f
",ans);
}